Systems including electromechanical polymer sensors and actuators

ABSTRACT

A localized multimodal haptic system includes one or more electromechanical polymer (EMP) transducers, each including an EMP layer, such as an electrostrictive polymer active layer. In some applications the EMP transducer may perform an actuator function or a sensor function, or both. The EMP polymer layer has a first surface and a second surface on which one or more electrodes are provided. The EMP layer of the EMP actuator may be 5 microns thick or less. The EMP transducers may provide local haptic response to a local a stimulus. In one application, a touch sensor may be associated with each EMP transducer, such that the haptic event at the touch sensor may be responded to by activating only the associated EMP transducer. Furthermore, the EMP transducer may act as its own touch sensor. A variety of haptic responses may be made available. The EMP transducers may be used in various other applications, such as providing complex surface morphology and audio speakers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to transducer; in particular, the presentinvention relates to transducers that based on electromechanical polymer(EMP) layers, and designed for such applications as controllablestructures, high-definition haptic feedback responses, audio speakers,or pressure sensors.

2. Discussion of the Related Art

Transducers are devices that transform one form of energy to anotherform of energy. For example, a piezoelectric transducer transformsmechanical pressure into an electrical voltage. Thus, a user may use thepiezoelectric transducer as a sensor of the mechanical pressure bymeasuring the output electrical voltage. Alternatively, some smartmaterials (e.g., piezoceramics and dielectric elastomers (DEAP)) deformproportionally in response to an electric field. An actuator maytherefore be formed out of a transducer based on such a smart material.Actuation devices based on these smart materials do not requireconventional gears, motors, and cables to enable precise articulationand control. These materials also have the advantage of being able toexactly replicate both the frequency and the magnitude of the inputwaveform in the output response, with switching time in the millisecondrange.

For a smart material that has an elastic modulus Y, thickness t, widthw, and electromechanical response (strain in plane direction) S₁, theoutput vibration energy UV is given by the equation:UV=½Y t w S₁ ²  (1)

DEAP elastomers are generally soft, having elastic moduli of about 1MPa. Thus, a freestanding, high-quality DEAP film that is 20 micrometers(μm) thick or less is difficult to make. Also, a DEAP film provides areasonable electromechanical response only when an electric field of 50MV/m (V/μm) or greater is applied. Thus, a DEAP type actuator typicallyrequires a driving voltage of 1,000 volts or more. Similarly, a DEAPtype sensor typically requires a charging voltage of 1,000 volts ormore. In a handheld consumer electronic device, whether as a sensor oras an actuator, such a high voltage poses safety and cost concerns.Furthermore, a DEAP elastomer has a low elastic modulus. As a result, toachieve the strong electrical signal output needed for a handheld deviceapplication requires too thick a film. The article, “Combined DrivingSensing Circuitry for Dielectric Elastomer Actuators in MobileApplications,” by M. Matsek et al., published in Electroactive PolymerActuators and Devices (EAPAD) 2011, Proc. Of SPIE vol. 7975, 797612,discloses providing sensor functions in dielectric elastomer stackactuators (DESA). U.S. Pat. No. 8,222,799 to Polyakov, entitled “SurfaceDeformation Electroactive Polymer Transducers,” also discloses sensorfunctions in dielectric elastomers.

Unlike a DEAP elastomer, a piezoceramic material can provide therequired force output under low electric voltage. Piezoelectricmaterials are crystalline materials that become electrically chargedunder mechanical stress. Converse to the piezoelectric effect isdimensional change as a result of imposition of an electric field. Incertain piezoelectric materials, such as lead zirconate titanate (PZT),the electric field-induced dimensional change can be up to 0.1%. Suchpiezoelectric effect occurs only in certain crystalline materials havinga special type of crystal symmetry. For example, of the thirty-twoclasses of crystals, twenty-one classes are non-centrosymmetric (i.e.,not having a center of symmetry), and of these twenty-one classes,twenty classes exhibit direct piezoelectricity. Examples ofpiezoelectric materials include quartz, certain ceramic materials,biological matter such as bone, DNA and various proteins, polymers suchas polyvinylidene fluoride (PVDF) and polyvinylidenefluoride-co-trifluoroethylene [P(VDF-TrFE)]. For further information,see, for example, the article “Piezoelectric Transducer Materials”, byH. JAFFE and D. A. BERLINCOURT, published on pages 1372-1386 ofPROCEEDINGS OF THE IEEE, VOL. 53, No. 10, October, 1965.

The strain of a piezoelectric device is linearly proportional to theapplied electric field E:S₁˜E  (2)

As illustrated in equation (2), when used in an actuator device, apiezoelectric material generates a negative strain (i.e., shortens)under a negative polarity electric field, and a positive strain (i.e.,elongates) under a positive electric field. However, piezoceramicmaterials are generally too brittle to withstand a shock load, such asthat encountered when the device is dropped.

Piezoceramics and dielectric elastomers change capacitance in responseto a mechanical deformation, and thus may be used as pressure sensors.However, as mentioned above, DEAP elastomers are generally soft, havingelastic moduli of about 1 MPa. Thus, a freestanding, high-quality DEAPfilm that is 20 micrometers (μm) thick or less is difficult to make.

Unlike the piezoelectric materials that require a special type ofcrystal symmetry, some materials exhibit electrostrictive behavior, suchas found in both amorphous (non-crystalline) and crystalline materials.“Electrostrictive” or “electrostrictor” refers to a strain behavior of amaterial under an electric field that is quadratically proportional tothe electric field, as defined in equation (3)S₁˜E²  (3)

Therefore, in contrast to a piezoelectric material, an electrostrictiveactuator always generates positive strain, even under a negativepolarity electric field (i.e., the electrostrictive actuator onlyelongates in the direction perpendicular to the imposed field), with anamplitude that is determined by the magnitude of the electric field andregardless of the polarity of the electric field. A description of someelectrostrictive materials and their behavior may be found, for example,in the articles (a) “Giant Electrostriction and relaxor ferroelectricbehavior in electron-irradiated poly(vinylidenefluoride-trifluoroethylene) copolymer”, by Q. M. Zhang, et al, publishedin Science 280:2101(1998); (b) “High electromechanical responses interpolymer of poly(vinylidenefluoride-trifluoroethylene-chlorofluoroethylene)”, by F. Xia et al,published in Advanced Materials, 14:1574 (2002). These materials arebased on electromechanical polymers. Some further examples of EMPs aredescribed, for example, in U.S. Pat. Nos. 6,423,412, 6,605,246, and6,787,238. Other examples include the EMPs whose compositions disclosedin pending U.S. patent application Ser. No. 13/384,196, filed on Jul.15, 2009, and the EMPs which are blends of the P(VDF-TrFE) copolymerwith the EMPs disclosed in the aforementioned U.S. patents.

To achieve a substantially linear response and mechanical strains of,say, up to four (4) percent, in a longitudinal or transverse direction,the electrorestrictive EMPs discussed above requires an electric fieldintensity between 50 to 100 MV/m. In the prior art, to provide adequatemechanical strength and flexibility, the polymer films are at least 20μm thick. As a result, an actuator based on such an electrostrictive EMPrequires an input voltage of about 2000 volts. Such a voltage istypically not available in a mobile device.

Polyvinylidene difluoride (PVDF) andpoly[(vinylidenefluoride-co-trifluoroethylene (P(VDF-TrFE)) arewell-known ferroelectric sensor materials. However, these materialssuffer from low strain, and thus perform poorly for many applications,such as keys on a keyboard. An EMP sensor based on a high modulus, highstrain material is therefore desired.

One area that EMPs find application is haptics. In this context, theterm “haptics” refers to tactile user input actions. As softwareapplications in portable electronics devices (e.g., cellular telephones,e-readers and tablets) have become more numerous and more diverse,greater data manipulation capabilities are required. In these devices,to interact with the software applications, users prefer the touchscreen than secondary tethered input devices (e.g., mechanicalkeyboards). A touch screen is also more intuitive, as compared to otherinput devices, which may require user training and some requisite motoragility. However, typing on a virtual keyboard displayed on the limitedspace of a touch screen is necessarily slow and error-prone, as userdoes not receive the familiar “confirmation” of action of a mechanicalkeyboard.

The deficiency of the virtual keyboard on a touch screen can be overcomeusing haptics. A haptics-enabled touch screen may generate an immediatehaptic feedback vibration when the touch screen is activated by userinput. The feedback vibration makes the virtual element displayed on thetouch screen more physical and more realistic. In a portable device(e.g., a mobile telephone), a haptic feedback action can reduce bothuser input errors and stress, allow a higher input speed, and enable newforms of bi-directionally interactions, Haptics is particularlyeffective for touch screens that are used in noisy or visuallydistracting environments (e.g., a battlefield or a gaming environment).For soldiers operating electronics or machines that uses multimodal ormultisensory interactions (e.g., together with visual and auditorysensations), haptics can reduce input error rates and improve responsespeed. Similar advantages can be achieved by gamers using handheld videogame devices.

A handheld device with basic haptics typically generatessingle-frequency, single-amplitude vibrations. In such a device, anactuator is typically mounted at a corner of the device casing, so as tomaximize the vibration felt by the user holding the device. Such anarrangement, however, generates a vibration throughout the entiredevice, rather than locally (i.e., at the point where the user's fingercontacts the device).

Recently proposed high-definition (HD) haptics may provide significantlymore tactile information to a user, such as texture, speed, weight,hardness, and damping. HD haptics uses frequencies that may be variedbetween 50 Hz to 400 Hz to convey complex information, and to provide aricher, more useful and more accurate haptic response. Over thisfrequency range, a user can distinguish feedback forces of differentfrequencies and amplitudes. Such a capability is applicable to typing ona HD haptics-enabled smart telephone that has a touch screen. In such adevice, the feedback vibration is expected to be controlled by software.For a user to experience a strong feedback sensation, HD haptics in thisfrequency range, switching times (i.e., rise and fall time) betweenfrequencies of 40 milliseconds (ms) or less are required. The ability toprovide such HD feedback vibrations in the 50 Hz to 400 Hz band,however, is not currently available. In the prior art, a typical devicehaving basic haptics has an output magnitude that varies with thefrequency of the driving signal. Specifically, the typical deviceprovides a greater output magnitude at a higher frequency from the sameinput driving amplitude. For example, if a haptic driving signalincludes two equal-magnitude sine waves at two distinct frequencies, theoutput vibration would be a superposition of two sine waves of differentmagnitudes, with the magnitudes being directly proportional to therespective frequencies. Such a haptic response is not satisfactory.Therefore, a compact, low-cost, low-driving voltage, and robust HDhaptics actuation device is needed.

Haptic responses need not be limited to 50 Hz to 400 Hz vibrations. Atlower frequency, a mechanical pressure response may be appropriate.Vibrations in the acoustic range can be made audible. A haptic responsethat can be delivered in more than one mode of sensation (e.g.,mechanical pressure, vibration, or audible sound) is termed“multimodal.” DEAP films or piezoelectric materials cannot provide theelastic moduli, strain, and robustness appropriate for multimodal hapticresponses over the relevant frequency range.

SUMMARY OF THE INVENTION

According to one embodiment of the present invention, a localizedmultimodal haptic system includes one or more electromechanical polymer(EMP) transducers, each including one or more EMP layers, such as anelectrostrictive polymer active layer. In some applications the EMPtransducer may perform an actuator function or a sensor function, orboth. The EMP polymer layer has a first surface and a second surface onwhich one or more electrodes are provided. The EMP layer of the EMPactuator may be 10 microns thick or less. The EMP transducers mayprovide local haptic response to a local stimulus. In one application, atouch sensor may be associated with each EMP transducer, such that thehaptic event at the touch sensor may be responded to by activating onlythe associated EMP transducer. Furthermore, the EMP transducer may actas its own touch sensor. A variety of haptic responses may be madeavailable.

According to one embodiment of the present invention, EMP transducersare provided for use in localized multimodal tactile feedbackapplications. For such applications, an EMP transducer provides highstrains, vibrations or both under control of an electric field. Forexample, with an application of a DC voltage, the EMP transducer maybend or deform a deformable surface, so as to form keys of a physicalkeyboard. Furthermore, the EMP transducer can generate strong vibrationsusing an AC voltage. When the AC voltage falls within the acousticrange, the EMP transducer can generate audible sound, therebyfunctioning as an audio speaker. Thus, the EMP actuator of the presentinvention can provide a multimodal haptic response (e.g., generatingdeformable surface, vibration, or audible sound, as appropriate). Inaddition, the EMP transducer can also serve as a touch sensor, as amechanical pressure applied on the EMP transducer can induce ameasurable electrical voltage output. Therefore, the EMP transducer mayserve as both a sensor and an actuator.

According to another embodiment, an EMP transducer of the presentinvention may also generate a temperature change through theelectrocaloric effect described, for example, in the article “LargeElectrocaloric Effect in Ferroelectric Polymers Near Room Temperature,”by Neese, et al, published on Science, Vol. 321 no. 5890 pp. 821-823,2008. The electrocaloric effect may be exploited to generate a coolingor heating effect to a user in a tactile system. In such an application,when an electric field is applied across an EMP transducer, thetemperature of the EMP transducer increases due to a reduced entropy.Conversely, when the electric field is reduced or turned off, thetemperature of the EMP transducer decreases due to increased entropy.

According to one embodiment of the present invention, an EMP transducercan also be fabricated in fabrics that can be provided in items ofclothing. Such EMP transducer thus may provide clothing with multimodalfunctions.

Because of their flexibility and their ease in manufacturing, EMPtransducers can be made very small even on a consumer device (e.g., thetouch surface of a cellular telephone). As a result, tactile feedback inresponse to touch by a human finger may be localized to an area in theimmediate vicinity of the touch stimulus, thereby offering a strongersensation and a finer resolution. This ability to concentrate thetactile feedback to a localized zone under the user finger can alsoreduce the device's power requirement, as the action required may beconfined to a small zone associated with the finger, without involvingthe entire device.

According to one embodiment of the present invention, when an excitationsignal is applied across the electrodes of an EMP layer, the EMP layerelongates (i.e., it provides an electrostrictive response). Since thepassive substrate's dimension remains unchanged, the EMP layer'selongation bends the EMP actuator that is associated with the electrodesand the substrate. The EMP layer is charged by the excitation signal.The excitation signal may have a frequency in a frequency range withinthe human acoustic range. In response to the excitation signal, theassociated EMP actuator vibrates at substantially the frequency of theexcitation signal. The frequency range may be between 0 Hz (i.e., DC) to10,000 Hz, depending on the EMP actuator's application. For example,when the EMP actuator is used to provide a deformable surface, thefrequency can vary from 0 Hz (DC) to 50 Hz; when the EMP actuator isused to provide a haptic feedback, the frequency may be in the range of50 Hz to 400 Hz; and when the EMP actuator is used to provide certainacoustic functions, the frequency can be in the range of 400 Hz to10,000 Hz. The vibration of the EMP actuator may provide an audiblesound. The EMP actuator disclosed herein may have a response latencyrelative to the excitation signal of less than 40 milliseconds. Inaddition, the EMP actuator may have a decay time of less than 40milliseconds. The EMP layer may have an elastic modulus greater than 500MPa at 25° C. and an electromechanical strain greater than 1%, whenexperiencing an electric field of greater than 100 MV/m.

According to one embodiment of the present invention, the EMP actuatorpreferably deforms with an acceleration of greater than 10 Gs in someapplications. To achieve the preferred acceleration, the excitationsignal may include a DC offset voltage in a range between 25-75 volts.The DC offset voltage may provide an electric field of greater than 10volts per micron. Further, the excitation signal may include analternating voltage component having a peak-to-peak range that is lessthan 300 volts, for example.

According to one embodiment of the present invention, one or more of theEMP actuators of a haptic system may be attached to a substrate, whichmay be provided above or underneath a surface of a touch-sensing device,for example. The substrate may be rigid or flexible, and may be providedby a thin glass or plastic material. The substrate may be a graphicaldisplay on a handheld device. Such a substrate may be 1000 microns thickand include a large number of picture elements (pixels) provided on onesurface. The EMP actuators may be arranged in a regular configuration,such as a regular 2-dimensional grid or array. The substrate may be atouch screen, such as the type of touch screens used in mobiletelephones. In that application, one or more of the EMP actuators areactuated to provide haptic feedback in response to an input signalcorresponding to a touch action by a user on the touch screen.

Unlike current haptics system which typically vibrates the entireelectrical device, which is often rigid, the EMP actuator-enabledhaptics can vibrate directly under the point of contact (e.g., a user'sfinger). In one embodiment, an array or grid of EMP actuators areprovided, in which only the actuator under the touch is selectivelyactivated, thereby providing a “localized” haptics feedback. When theEMP actuators are arranged in sufficiently close vicinity of each other,the haptic system may take advantage of haptic responses that aresuperimposed for constructive interference. In some embodiments, thesubstrate may vibrate in concert with the EMP actuators.

According to one embodiment of the present invention, the EMP actuatorsof the haptic system may be arranged in a non-regular configuration,such as in the form of the key layout of a QWERTY keyboard. When the EMPactuators are activated using a steady DC (0 Hz), the surface can bedeformed to provide a regular physical keyboard. In that embodiment,when it is detected that a specific key is pressed by a user, anexcitation signal may be provided to cause the associated EMP actuatorto vibrate, so as to confirm to the user that the user's typing actionhas been detected.

According to one embodiment of the present invention, multiple EMPactuators of the haptic system may be arranged in an array or gridconfiguration on surface. When the EMP actuators are selectivelyactivated, concave or convex bending of the surface at the EMP actuatorsresults. In this manner, the surface can be deformed to allow certaingraphical information to be presented.

According to one embodiment of the present invention, the EMP actuatorof the haptic system may be activated by a high frequency signal havingone or more frequency components in the range of 400 Hz to 10,000 Hz.The high frequency vibration of the EMP actuator (or the EMP actuatortogether with the substrate) can generate an audible acoustic signal.The EMP actuator can therefore act as an audio speaker. According toanother embodiment of the present invention, multiple EMP actuators thatare capable of performing such audio speaker function may be arranged inan array or grid on the haptics surface. As the EMP actuators arearranged in an array configuration, the haptics surface can serve aslocalized or directional speakers. When multiple actuators areselectively activated, the haptics surface can provide stereo orsurround sound function.

According to one embodiment of the present invention, a controller maybe used to provide control signals to the electrodes of each EMPactuator, such that each EMP actuator is individually controlled. TheEMP actuators may be positioned in predetermined locations, such thatthe EMP actuators may be controlled to function, for example, as aphased array. The phased array focuses the haptic responses of the EMPactuators to a desired location. In another embodiment, the EMPactuators are positioned at predetermined locations so as to maximizedisplacements at one or more predetermined locations. One of the EMPactuators may achieve an acceleration magnitude of greater than 0.5 G inresponse to an excitation signal of a frequency between 50 Hz and 400Hz.

The terms “haptics system” or “haptics surface”, as used hereinencompasses many variations and modifications. For example, the surfaceon which EMP actuators may be provided may be flat or planar, curved,cylindrical, spherical, parabolic, any non-planar, or three-dimensionstructure. The flexibility of the EMP actuators makes it possible tofabricate them in three-dimensional structures and form factors.

The haptic system of the present invention is especially applicable to amobile electronic computational or communication device, such as amobile telephone, a tablet computer, or a notebook computer.

The present invention may also provide an electromechanical systemcomprising one or more electromechanical polymer (EMP) sensors. Eachsuch sensor may include (a) at least one EMP layer (preferably, manysuch layers) that includes an electrostrictive active layer, the EMPpolymer layer having a first surface and a second surface; (b) one ormore electrodes provided on at least one of the first surface and thesecond surface; and (c) a force receiving surface structurally connectedwith the EMP layer for transmitting an external force to the EMP layer.Each EMP layer may be 10 microns thick or less. The electromechanicalsystem may include a rigid substrate bonded to one side of one of theEMP sensors, and wherein the force receiving surface being provided onthe side of the EMP sensor opposite to the side of the EMP sensor bondedto the rigid substrate. The substrate may be bonded to the EMP sensor byan acrylate adhesive. Alternatively, the substrate may be bonded to theEMP sensor by thermal lamination. The force receiving surface may beprovided on a compliant metal plate attached to one side of one of theEMP sensors. The external force exerted on the force receiving surfaceresults in an electrical signal being induced across a selected pair ofthe electrodes, the electrical signal is typically between 1 to 5 volts.

According to one embodiment of the present invention, theelectromechanical system further includes an EMP actuator and a controlcircuit that receives the electrical signal from the selected pair ofthe electrodes and which provides an output signal to the EMP actuator.The output signal causes the EMP actuator to vibrate. The vibration ofthe EMP actuator provides a haptics feedback or an audible sound.

According to one embodiment of the present invention, theelectromechanical system includes a source of voltage that charges theEMP layer of each EMP sensor to a quiescent state prior to the forcereceiving surface transmitting the external force to the EMP layer. Theelectromechanical system may further include means for determining achange in charged state in the EMP sensor (e.g., a voltage change acrossthe terminals, or a change in charge held in the EMP sensor), such as aresistor connected in series with the EMP sensor between terminals ofthe source voltage. In that example, the electromechanical system mayfurther include a sensing circuit connected across the resistor, thesensing circuit being sensitive to a voltage change across the resistor.Alternatively, the sensing circuit may be connected in series with theresistor, the sensing circuit being sensitive to a current flowing inthe resistor.

According to one embodiment of the present invention, one or more of theEMP sensors are configurable to serve as EMP actuators which provide amechanical output in response to an electrical signal being imposedacross the electrodes of the one or more of the EMP sensors.

The present invention is better understood upon consideration of thedetailed description below in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows storage modulus of a stretched film, as measured using adynamic mechanical analyzer at 1 Hz over a temperature range of −20° C.to 50° C.

FIG. 2 shows the strain S₁ of an EMP actuator with a stretched EMP film,as measured in the stretching direction, as a function of the appliedvoltage.

FIGS. 3( a) and 3(b) show, according to one embodiment of the presentinvention, single-layer EMP transducer 100 that includes single layer140 of an electrostrictive polymer and two electrodes 130 deposited orbonded to opposite sides thereof.

FIG. 4 shows multi-layer EMP transducer 400 that includes electrodes 130on both sides of each EMP layer 140, according to one embodiment of thepresent invention.

FIG. 5 shows multi-layer EMP transducer 500 that includes electrode 130formed only on one side of each EMP layer 140, according to oneembodiment of the present invention.

FIG. 6 shows multi-layer EMP transducer 600 that includes multipleunits, each unit including EMP layer 140 and electrode 130, beingthermally bonded together, according to one embodiment of the presentinvention.

FIG. 7 shows EMP actuators 512 forming a 1×2 array bonded to substrate520.

FIG. 8 shows single EMP actuator 510 bonded to substrate 520.

FIG. 9 shows a 1×3 array of actuators 510 bonded to substrate 520.

FIG. 10 shows 15 EMP actuators 830 in 5 by 3 array bonded to substrate520.

FIG. 11 shows six EMP actuators 830 in a 3 by 2 array bonded tosubstrate 520.

FIG. 12 shows the haptic responses of EMP actuators 510 of FIG. 7.

FIG. 13 shows the haptic responses in 5 EMP actuators 830 configured inthe 5 by 3 array of FIG. 10, in accordance with one embodiment of thepresent invention.

FIG. 14 shows haptic responses of all 15 EMP actuators 830 in the 5×3array of FIG. 10, in accordance with one embodiment of the presentinvention.

FIG. 15 shows multi-layer EMP actuator 1500 being bonded by an acrylateadhesive to a 250 μm thick polyethylene terephthalate (PET) filmsubstrate, according to one embodiment of the present invention.

FIG. 16 shows multi-layer EMP actuators 1600, arranged in a 3×2 array,being adhesively bonded to PET substrate 1601, in accordance with oneembodiment of the present invention.

FIG. 17 shows the triangular waveform of a driving electric field on amulti-layer EMP actuator; the driving electric field has a 50 V DCoffset voltage and a 200 V peak-to-peak voltage.

FIG. 18 shows the output accelerations of a multi-layer EMP actuatorunder DC-offset voltages of 0 volts, 25 volts, 50 volts and 75 volts.

FIG. 19 shows surface accelerations for multi-layer actuators comprisingdifferent number of component EMP layers, as a function of input signalfrequency.

FIGS. 20( a)-(c) illustrate the effect of stacking EMP actuators ofdifferent thicknesses and sizes, in accordance with one embodiment ofthe present invention.

FIGS. 21( a) and 21(b) shows conceptually how an EMP sensor operates,according to one embodiment of the present invention.

FIGS. 22( a) and 22(b) show EMP sensor 2400 provided on the surface ofthin compliant film 401 (e.g., a thin aluminum or steel film), inaccordance with one embodiment of the present invention.

FIGS. 23( a) and 23(b) show EMP sensor 2500 provided on the surface ofrigid substrate, in accordance with one embodiment of the presentinvention.

FIGS. 24( a) and 24(b) show EMP sensor 2600 placed between the surfacesof two compliant layers 601 and 602, in accordance with one embodimentof the present invention.

FIG. 25 shows schematic circuit 2700 in which EMP sensor 2701 is used,in accordance with one embodiment of the present invention.

FIG. 26 shows schematic circuit 2800 in which EMP sensor 2801 is used,in accordance with one embodiment of the present invention.

FIG. 27 shows schematic circuit 2900 in which control circuit 2901receives from EMP sensor/actuator 2902 sensing signal 2903,representative of the tactile pressure experienced at EMPsensor/actuator 2902 and provides a haptic response through actuatingsignal 2904, in accordance with one embodiment of the present invention.

FIG. 28 illustrates system 1000 in which EMP transducer 1004 performsboth actuation and sensing operations, in accordance with one embodimentof the present invention.

FIGS. 29( a) and 29(b) each show a suitable key movement mechanism ofsuch an EMP actuated keyboard, in accordance with one embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The electromechanical polymer (EMP) transducers of the present inventiondisclosed herein are electrostrictive, rather than piezoelectric. Someexamples of the electromechanically active polymers incorporated in theEMP transducers of the present invention include P(VDF-TrFE) modified byeither high energy density electron irradiation or by copolymerizationwith a third monomer. Such a modification lead to significantperformance change; namely, the EMP loses its piezoelectric andferroelectric behaviors and become an “electrostrictive” or “relaxorferroelectric” material. The resulting EMP actuators respond to animposed electric field by elongating in a direction perpendicular to theelectric field, regardless of the field polarity. Typically, the EMPactuator of the present invention may generate a more than 1% strainunder an electric field of 100 MV/m, which is significantly higher thanthe typical piezoelectric materials, such as lead zirconate titanate(PZT), a piezoelectric ceramic material.

The term “relaxor ferroelectric” is sometimes used with respect to EMPsto emphasize the absence of hysteresis in their strain response andtheir charge accumulation under an alternating current (AC) electricfield. Therefore, the EMP transducers disclosed herein may also bereferred to as “relaxor ferroelectric” or “electrostrictive”transducers. An electromechanical polymer (EMP) transducer typicallyincludes an EMP layer that comprises an electrostrictive polymer activelayer and electrodes bonded thereto. With the electrostrictive polymeractive layer being less than 10 microns thick, the present inventionprovides EMP actuators that may be actuated at a low driving voltage(e.g., 300 volts or less; preferably, 150 volts or less) suitable foruse in a wide variety of consumer electronic devices, such as mobiletelephones, laptops, ultrabooks, and tablets.

When an external electric field is imposed across the EMP layer, the EMPlayer becomes charged. The EMP layer thus behaves electrically as acapacitor. (The electric field also provides the electrostrictiveresponse discussed above). The present invention provides EMP sensorsthat may be operated at a low charging voltage (e.g., 300 volts or less;preferably, 150 volts or less) suitable for use in a wide variety ofconsumer electronic devices, such as mobile telephones and tablets. Insome embodiments, EMP sensors disclosed herein may also serve as EMPactuators.

FIGS. 3( a) and 3(b) show, according to one embodiment of the presentinvention, single-layer EMP transducer 100 that includes a single EMPlayer (i.e., EMP layer 140) of a relaxor ferroelectric fluoropolymer andtwo electrodes 130 deposited or bonded to opposite sides the single EMPlayer. Passive substrate 110 is bonded to one side of EMP transducer 100by adhesive 120. Alternatively, passive substrate 110 may be bonded toEMP transducer 100 by thermal lamination. EMP layer 140, electrodes 130and adhesive 120 may have various thicknesses. For the applicationsdisclosed in this detailed description, EMP layer 140 may be 0.1-10 umthick. Typically, EMP layer 140 may be about 1 um to about 7 um thick(e.g., 2-5 μm thick), preferably about 3 μm thick. EMP layer 140 neednot have uniform thickness. Adhesive 120 may be up to about 0.5 μmthick. Although EMP layer 140 is shown in FIG. 3( a) as planar, EMPlayer 140 may have any of a wide variety of non-planar shapes (e.g.,cylindrical, spherical, or parabolic). Single layer transducer 100 ofFIG. 3( a) illustrates a unimorph design, in which EMP transducer 100elongates in one direction under an electrical voltage provided acrossits thickness, while substrate 110 does not change its dimension. Asshown in FIG. 3( b), when a voltage is applied across EMP transducer100—which is of a unimorph design—EMP layer 140 bends in a concavemanner. By suitably positioning a number of EMP transducers that areindependently controlled (e.g., in an array, on a grid, at one or morecorners of a polygonal area, overlapping, or in any suitable organizedmanner), different shapes or surface morphologies can be achieved.

According to a second embodiment of the present invention, an EMPtransducer may include multiple electrostrictive polymer active layersand electrode layers configured in a stack to enable a cumulative forceeffect. The EMP layers and electrodes may be arranged so that theelectrodes are electrically connected in parallel. FIGS. 4-6 showvarious configurations of multi-layer EMP transducers. The multiple EMPlayers with electrodes may be bonded together by adhesive or by thermallamination. Adjacent EMP layers may share an electrode. In someembodiments, the EMP layers may be 1-10 microns thick, formed out of1-1000 single EMP layers.

Bimorph transducers can also be produced using the EMP layers withindependently controlled electrodes. For example, two EMP transducerswith independent controls and power supplies can be bonded together toform such a bimorph transducer. An optionally passive layer may beincluded between the two EMP transducers. When one of the EMPtransducers (“first EMP transducer”) is activated while the other EMPtransducer (“second EMP transducer”) is not, the bimorph device bendstowards the second EMP transducer. On the other hand, when the secondEMP transducer is activated, while the first EMP transducer is notactivated, the bimorph device bends towards the first EMP transducer.Thus, a bimorph EMP transducer device can be controlled to bend ineither direction.

FIG. 4 illustrates multi-layer EMP transducer 400 that includeselectrodes 130 formed on both sides of each EMP layer 140, according toone embodiment of the present invention. Thus, multilayer EMP transducer400 may be provided by stacking multiple single-layer EMP transducers,each exemplified, for example, by EMP transducer 100 of FIG. 3( a). Ithas been determined the stacked EMP transducers together provide agreater surface deformation than the surface deformation provided by asingle-layer EMP transducer of the same total thickness. Adhesive 120may be used to bond electrodes 130 of adjacent EMP transducers.

FIG. 5 illustrates multi-layer EMP transducer 500 that includeselectrode 130 formed only on one side of each EMP layer 140, accordingto one embodiment of the present invention. As shown in FIG. 5, each EMPlayer 140 is bonded by adhesive 120 to electrode 130 of an adjacent EMPlayer 140.

FIG. 6 illustrates multi-layer EMP transducer 600 that includes multipleunits, each unit including EMP layer 140 and electrode 130, beingthermally bonded together, according to one embodiment of the presentinvention. The EMP layers may be the same or different. The EMP layersalso may have the same or different thicknesses. The multilayer EMPactuator illustrated in FIG. 6 employs alternating layers of EMP layer140 and electrode 130 thermally bonded to both sides of EMP layer 140.

EMP layer 140 of any EMP transducer discussed herein may be preprocessed(e.g., uniaxially or biaxially stretched, conventionally or otherwise,or having electrodes formed thereon) to condition the EMP layer'selectromechanical response to an applied external field. A biaxiallystretched actuator can deform in all directions in the plane of the axesof stretching, resulting in a dome-shaped deformation suitable for useas input keys or buttons, or braille text. A stretched EMP layertypically may be annealed at about 80° C. to about 130° C. When the EMPactuators are activated using a steady DC (i.e., 0 Hz), the surface canbe deformed to provide a regular physical keyboard (e.g., a QWERTYkeyboard). When a pressure sensor provided in the vicinity (e.g., atouch-sensing surface) detects that a specific key is pressed by a user,an excitation signal may be provided to cause the associated EMPactuator to vibrate, as a haptics response to confirm to the user thatthe user's typing action has been detected.

Electrodes 130 of any EMP transducers discussed herein may be formedusing any suitable electrically conductive materials, such astransparent conducting materials (e.g., indium tin oxide (ITO) ortransparent conducting composites, such as indium tin oxidenanoparticles embedded in a polymer matrix). Other suitable conductivematerials include carbon nanotubes, graphenes, and conducting polymers.Electrodes 130 may also be formed by vacuum deposition or sputteringusing metals and metal alloys (e.g., aluminum, silver, gold, orplatinum). Nanowires that are not visible over a graphical display layermay also be used.

In some embodiments, the EMP transducers may be made transparent whentransparent electrodes are used. Transparent EMP transducers can beused, for example, in conjunction with a display or touch surface (e.g.,placed on top of the display or surface) without detriment to theperformance of the display or touch surface. In other embodiments, usingsuitable electrodes, EMP transducers can be made semi-transparent. Suchsemi-transparent EMP transducers are suitable for use in applicationswhich require certain level of light to be transmitted. One example of asuitable application for semi-transparent EMP transducers may be askeyboards with backlit light. In yet other embodiments, EMP transducerscan be opaque. Such opaque EMP transducers may be used in applicationswhere light transmission is not necessary.

The present invention may be used to provide keyboards or other userinterface devices in consumer electronics, which continue to becomesmaller and thinner. Low-profile, thin keyboards are desired for usewith many information processing devices (e.g. tablet computers,ultrabook and MacBook Air). Because the EMP transducers of the presentinvention can be made very thin, according to one embodiment of thepresent invention, a keyboard based on EMP transducers may be providedwhich includes physical key movements in the manner of a conventionalkeyboard. FIGS. 29( a) and 29(b) each show a suitable key movementmechanism of such an EMP actuated keyboard, in accordance with oneembodiment of the present invention. A haptic response may be providedas confirmation of receipt of the user's key activation in the user'styping. In this regard, the EMP actuators may replace the springmechanism in a classical keyboard, enabling a low-profile thin keyboard,while still providing the desirable key travel distance in aconventional keyboard that a user expects. When at rest, keys in such akeyboard are recessed, with the EMP transducer being in a flat,quiescent position in the thin keyboard. Upon activation, which occurswhen the keyboard is readied for typing, the EMP transducers areactivated to lift each key by a distance of 0.1 mm to 10 mm. When a userpresses a key, the pressure of the user's finger depresses the keyagainst the EMP transducer, perhaps by a distance roughly equal to thedistance of the activation lift, by overcoming the upward pressure inthe activated transducer. In this manner, the key that is pressedtravels the conventional key travel distance, as in a conventionalkeyboard. When the user releases the key, the activated EMP transducerreturns to the lifted position, ready in its charged state for the nextkey press. Alternatively, an electrical voltage that is controlled by acontroller may be provided on the EMP transducer to provide apredetermined force profile for an even richer user experience. As theEMP transducer has EMP active layers that are based on one or moredielectric electrostrictive polymers with high electrical resistance,such an EMP actuated keyboard requires little power, as power isdissipated only through tiny leakage currents.

As shown in FIG. 29( a), an EMP transducer 1102 is provided to supportkey or button 1103. EMP transducer 1102 is fixed to base structure orsubstrate 1101. Key 1103 may be mechanically connected to EMP actuator1102 by a rigid pillar. FIG. 29( a) shows EMP transducer 1102 in a reststate (shown in the upper half of the figure) and in an activated state(shown in the lower half of the figure). In the rest state, EMP actuator1102 is not activated. Upon activation by an electric field, i.e., whenEMP transducer 1102 is in the activated state, EMP transducer 1102pushes against fixed base structure 1101, bending to form a dome orbridge structure, thereby lifting key 1103. Since activated EMPtransducer 1102 asserts a blocking force that is proportional to theapplied electric field, when a user pushes key 1103 down with a forcethat is greater than the blocking force, key 1103 and EMP transducer1102 travels downward, even though EMP transducer 1102 remains activatedby the applied electric field. When the user lifts his finger, therebyreleasing key 1103, EMP transducer 1102 and key 1103 automaticallyreturns to the lifted position. For keyboard application, the EMPtransducers may be further controlled by electric field to provideadditional key travel.

FIG. 29( b) illustrates a second design using EMP transducers in akeyboard application. As shown in FIG. 29( b), two EMP transducers(collectively, EMP transducers 1102) lift key 1103 in the same manner asdescribed above in conjunction with FIG. 29( a), except that only oneend of each of EMP transducers 1102 is fixed to base structure orsubstrate 1101. In the rest position (shown in the upper half of FIG.29( b)), i.e., EMP transducers 1102 are not activated, EMP transducers1102 are flat and key 1103 is in a recessed position. Upon activation(shown in the lower half of FIG. 29( b)), i.e., when an electric fieldis applied across each of EMP transducers 1102, the free ends of EMPtransducers 1102 bend upwards to lift key 1103. In this second design,two or more EMP transducers may be used to lift each key of thekeyboard.

According to one embodiment of the present invention, the EMP actuatorsform on a deformable surface a refreshable braille display.

The EMPs suitable for use in components (e.g., EMP actuators employed inhaptic substrates and haptic devices disclosed herein) typically showvery high strain of about 1% or more under an electric field gradient of100 megavolts per meter or greater. (Strain is measured as the change inlength of an EMP layer as a percentage of the quiescent length.) The EMPlayers also may show elastic modulus of about 500 MPa or more at 25° C.,a mechanical vibrational energy density of 0.1 J/cm³ or more, adielectric loss of about 5% or less, a dielectric constant of about 20or more, an operating temperature of about −20° C. to about 50° C., anda response time of less than about 40 millisecond.

Suitable electrostrictive polymers for EMP layers 140 include irradiatedcopolymers and semi-crystalline terpolymers, such as those disclosed inU.S. Pat. Nos. 6,423,412, 6,605,246, and 6,787,238. Suitable irradiatedcopolymers may include high energy electron irradiatedP(VDF_(x)-TrFE_(1-x)) copolymers, where the value of x may vary between0.5 to 0.75. Other suitable copolymers may include copolymers ofP(VDF_(1-x)-CTFE_(x)) or P(VDF_(1-x)-HFP_(x)), where the value of x isin the range between 0.03 and 0.15 (in molar). Suitable terpolymers thatmay have the general form of P(VDF_(x)-2nd monomer_(y)-3rdmonomer_(1-x-y)), where the value of x may be in the range between 0.5and 0.75, and the value of y may be in the range between 0.2 and 0.45.Other suitable terpolymers may include P(VDF_(x)-TrFE_(y)-CFE_(1-x-y))(VDF: vinylidene fluoride, CFE: chlorofluoroethylene, where x and y aremonomer content in molar), P(VDF_(x)-TrFE_(y)-CTFE_(1-x-y)) (CTFE:chlorotrifluoroethylene), poly(vinylidenefluoride-trifluoroethylene-vinylidene chloride) (P(VDF-TrFE-VC)), wherex and y are as above; poly(vinylidenefluoride-tetrafluoroethylene-chlorotrifluoroethylene) (P(VDF-TFE-CTFE)),poly(vinylidene fluoride-trifluoroethylene-hexafluoropropylene),poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene),poly(vinylidene fluoride trifluoroethylene-tetrafluoroethylene),poly(vinylidene fluoride tetrafluoroethylene tetrafluoroethylene),poly(vinylidene fluoride-tri fluoroethylene-vinyl fluoride),poly(vinylideneflouride-tetrafluoroethylene-vinyl fluoride),poly(vinylidene flouride-trifluoroethyleneperfluoro(methyl vinylether)), poly(vinylidene fluoride-tetrafluoroethylene-perfluoro(methylvinyl ether)), poly(vinylidenefluoride-trifluoroethylene-bromotrifluoroethylene, polyvinylidene),poly(vinylidene fluoride-tetrafluoroethylene-chlorofluoroethylene),poly(vinylidene fluoride-trifluoroethylene-vinylidene chloride), andpoly(vinylidene fluoride tetrafluoroethylene vinylidene chloride),

Furthermore, a suitable EMP may be in the form of a polymer blend.Examples of polymer blends include of polymer blends of the terpolymerdescribed above with any other polymers. One example includes the blendof P(VDF-TrFE-CFE) with P(VDF-TrFE) or blend of P(VDF-TrFE-CTFE) withP(VDF-TrFE). Other examples of suitable polymer blends include a blendof P(VDF-TrFE-CFE) with PVDF or a blend of P(VDF-TrFE-CTFE) with PVDF.Irradiated P(VDF-TrFE) EMP may be prepared using polymeric material thatis itself already a polymer blend before irradiation.

According to one embodiment of the present invention, to form a EMPlayer, P(VDF-TrFE-CFE) polymer powder was dissolved in N,N-dimethylformamide (DMF) solvent at 5 wt. % concentration. The solutionwas then filtered and cast onto a glass slide to produce a 30 μm thickfilm. The film was then uniaxially stretched by 700% (i.e., the finalfilm length equals to 700% of the cast film length), resulting in 5 μmthick film. The stretched 5 μm thick film was further annealed in aforced air oven at 110° C. for two hours. FIG. 1 shows storage modulusof the resulting stretched film, as measured using a dynamic mechanicalanalyzer (e.g., DMA, TA DMA 2980 instrument) at 1 Hz over a temperaturerange of −20° C. to 50° C. As shown in FIG. 1, the stretched polymerfilm has a storage modulus of 685.2 MPa at 25° C. Thus, an EMP actuatormay be made by casting a layer of EMP polymer (e.g., a P(VDF-TrFE-CFE)or P(VDF-TrFE-CTFE) terpolymer). Such a film may be stretched andannealed at about 80 to about 130° C.

The stretched EMP film of FIG. 1 was metallized by sputtering 30 nmthick gold layers on both sides of the film. Various voltages wereapplied to the resulting EMP actuator and the changes in film length inthe direction parallel to stretching were measured. FIG. 2 shows strainS₁ of the EMP actuator in the stretching direction, as a function of theapplied voltage. As shown in FIG. 2, the stretched EMP film has strainS₁ of 0.48% at 40 MV/m and 2.1% at 100 MV/m.

An EMP transducer of the present invention may also generate atemperature change through the electrocaloric effect described, forexample, in the article “Large Electrocaloric Effect in FerroelectricPolymers Near Room Temperature,” by Neese, et al, published on Science,Vol. 321 no. 5890 pp. 821-823, 2008. The electrocaloric effect may beexploited to generate a cooling or heating effect to a user in a tactilesystem. In such an application, when an electric field is applied acrossan EMP transducer, the temperature of the EMP transducer increases dueto a reduced entropy. Conversely, when the electric field is reduced orturned off, the temperature of the EMP transducer decreases due toincreased entropy. Thus, the EMP transducer of the present invention mayserve as both an actuator and a cooling device at the same time. Thecooling effect may be utilized to provide the user special tactilefeedback.

Some EMP transducers exhibit a pyroelectric effect that can be used tosense temperature change. In such an EMP transducer, a change intransducer or environment temperature results in a change in a dimensionin the EMP transducer. The resulting change in its capacitance may bemeasured electrically (e.g., an electrical current or a change involtage resulting from the change in electric charge).

Table 1 shows the performance of actuators made with modified,P(VDF-TrFE)-based EMP (‘EMP”), dielectric elastomer and piezoceramics.

Elastomer Piezoceramics Property EMP DEAP (PZT 5H) Strain 2.0% at 5-10%at 0.1% at (Stretching 100 V/μm 100 V/μm 2 V/μm Direction) Young's >500~1 ~100,000 Modulus (MPa) Vibration >0.1 ~0.005 ~0.05 Mechanical EnergyDensity (J/cm³) Dielectric 35 3 2500 Constant Dielectric 5 5 2 Loss (%)Minimal Film 3 18 50 Thickness (μm) Voltage for 300 1800 100 ListedStrain Operating −20° C.~50° C. −20° C.~50° C. −50° C.~100° C.Temperature Response Time <1 <10 <0.1 (ms)

As shown in Table 1, an EMP layer made with modified, P(VDF-TrFE)-basedEMP has balanced electromechanical response and mechanical modulus. Theoutput vibration mechanical energy density of such an EMP layer is alsosignificantly higher than the elastomer DEAP and piezoceramic actuators.

FIGS. 7-11 show EMP actuators bonded on a substrate in variousconfigurations suitable for use in forming haptic surfaces in consumerelectronic devices. A haptic surface may be formed by bonding one ormore EMP actuators to a substrate that is part of or placed on a sensingsurface (e.g., a touch screen) of an electronic device, and connectingelectrical conductors to each EMP actuator to a voltage sourcecontrolled by the electronic device. As each EMP actuator may have avery small footprint, the haptic response provided may be localized tothe area of the small footprint. The haptic surface thus allows theelectronic device to respond to a user's input stimulation at a sensingsurface by providing “localized” haptic feedback, i.e., precisely at thepoint of input stimulation. As shown in FIG. 7, EMP actuators 512 in a1×2 array is bonded (e.g., by adhesive) to substrate 520. FIG. 8 showssingle EMP actuator 510 bonded to substrate 520. FIG. 9 shows a 1×3array of actuators 510 bonded to substrate 520. FIG. 10 shows 15 EMPactuators 830 in 5 by 3 array bonded to substrate 520. FIG. 11 shows sixEMP actuators 830 in a 3 by 2 array bonded to substrate 520.

The sensing surface may be provided, for example, on a graphical displaylayer, such as typically in a mobile telephone. In these arrangements,each EMP actuator may be actuated independently or in concert with otherEMP actuators. As explained below, the EMP actuators may excitestructural modes of the haptic surface within a desired haptic frequencyband. Also, the EMP actuators may be arranged to operate as a phasedarray to focus haptic feedback to a desired location. In one embodiment,the EMP actuators may be laminated on a thin glass or plastic substratethat is less than 1,000 μm thick. Such a haptic surface is sufficientlythin to effectively transmit a haptic event without significantlyattenuating the actuator output. Suitable substrate materials includetransparent materials such as glass, polycarbonate, polyethyleneterephthalate (PET), polymethyl methacrylate, polyethylene naphthalate(PEN), opaque material such as molded plastic, or mixtures thereof.Other suitable substrate materials include multi-component functionalsheets such LCD, OLED, PET and combinations thereof.

The EMP transducers may be provided a coating on the top surface or thebottom surface as an electrical insulation layer, as a force receivinglayer, or as a protection layer (e.g., to protect from exposuremoisture, water or air). The coating may be scratch-resistant, forexample, for durability. The coating may be a plastic formed by applyinga wet-coating or lamination, or an inorganic layer formed by vapordeposition. Examples of a suitable coating layer include silicone,silicon oxide, silicon nitride, fluoropolymers, acrylates, and PET.

The substrate, the EMP actuators and the electrical connectors typicallyare sufficiently flexible to be assembled into a haptic surface by thewell known roll-to-roll manufacturing process. In the “roll-to-roll”process, the steps of a manufacturing process are performed on acontinuous moving belt that originates from a feed reel.

EMP actuators disclosed herein may be actuated by low driving voltagesof less than about 300 volts (e.g., less than about 150 volts). Thesedriving voltages typically may generate an electric field of about 40V/um or more in the EMP layer of the EMP actuator. The EMP actuators maybe driven by a voltage sufficient to generate an electric field that hasa DC offset voltage of greater than about 10 V/μm, with an alternatingcomponent of peak-to-peak voltage of less than 300 volts. (Theexcitation signal need not be single-frequency; in fact, an excitationsignal consisting simultaneously of two or more distinct frequencies maybe provided.) The EMP actuators disclosed herein provide a hapticvibration of substantially the same frequency of frequencies as thedriving voltage. When the driving voltages are in the audio range (e.g.,up to 40,000 Hz, preferably 400-10000 Hz), audible sounds ofsubstantially those in the driving frequency or frequencies may begenerated. These EMP actuators are capable of switching betweenfrequencies within about 40 ms, and are thus suitable for use in HDhaptics and audio speaker applications. The EMP actuators are flexibleand can undergo significant movement to generate high electrostrictivestrains. Typically, a surface deformation application would useexcitation frequencies in the range between 0-50 Hz, a localized hapticapplication would use excitation frequencies in the range between 50-400Hz, and an audio application would use excitation frequencies in therange between 400-10,000 Hz, for example.

When driven under an AC signal, the waveform may be triangular,sinusoid, or any arbitrary waveform. In fact, the waveform can becustomized to generate any specific, desired tactile feedback. Forexample, the frequency of the waveform can be the same throughout theduration of a haptics event, or may be continuously changed. Thewaveform or the amplitude of the AC signal can also be the samethroughout the haptics event, or continuously changed.

FIGS. 12-14 illustrate the haptic responses in EMP actuators disclosedherein. For example, FIG. 12 shows the haptic responses of EMP actuators510 of FIG. 7. As shown in FIG. 12, substrate 520 deflects locally asEMP actuators 510 actuate in an extensional manner. EMP actuators 520may be controlled separately to maximize haptic output and to providetailored haptic response to the user.

FIG. 13 shows the haptic responses in five of EMP actuators 830,configured in the 5 by 3 array of FIG. 10. As shown in FIG. 13,substrate 520 locally deflects as EMP actuators 830 actuate in anextensional manner. Note that, each EMP actuator may be activated todeform the substrate on which it is situated to form an input key orbutton. Likewise, FIG. 14 shows haptic responses of all 15 EMP actuators830 in the 5×3 array of FIG. 10.

The EMP actuators disclosed herein have typical latency rise time (i.e.,the time between the EMP actuator receiving its activating input signalto the EMP actuator providing the mechanical haptic response) from lessthan about 5 milliseconds up to about 40 milliseconds. The EMP actuatorshave a typical decay time (i.e., the time between the EMP actuatorreceiving the cessation of the activating input signal to the EMPactuator's haptic response falling below the user's detectablethreshold) from less than about 5 milliseconds up to about 40milliseconds. The EMP actuators typically have an acceleration responseof greater than about 0.5 G to about 2.5 G over a frequency range ofabout 100 Hz to about 300 Hz.

FIG. 15 shows multi-layer EMP actuator 1501 being bonded by acrylateadhesive to a 250 μm thick polyethylene terephthalate (PET) filmsubstrate 1502, according to one embodiment of the present invention. Asshown in FIG. 15, PET film substrate 1502 is suspended in an open cavitybetween frame bottom 1503 and frame top 1504, secured by four bolts1505-1 to 1505-5 to provide a single-layer haptic surface. Electricalconnection 1506 allows a voltage to be supplied to EMP actuator 1501.

FIG. 16 shows multi-layer EMP actuators 1600, arranged in a 3×2 array,being adhesively bonded to PET substrate 1601, in accordance with oneembodiment of the present invention. Each multilayer EMP actuator may beformed, for example, by bonding together twenty 5 μm-thick, single-layerEMP actuators using acrylate adhesives. (Generally, a thinner EMP filmlayer requires a lesser driving electric field.) At a peak input voltageof 200 V, a multi-layer actuator in the array may achieve a peakaccelerations of greater than 4 G at a frequency within the frequencyrange between 125 Hz and 400 Hz. Over the same range, the averageacceleration would be greater than 1 G. FIG. 16 also shows theacceleration of each of multi-layer actuators 1600, measured as afunction of input signal frequency, using a shear accelerometer (e.g.,Model 352C65, PCB Piezotronics) at 25° C.

FIGS. 20( a)-(c) illustrate the effect of stacking EMP actuators ofdifferent sizes and thicknesses, in accordance with one embodiment ofthe present invention. FIGS. 20( a) and 20(b) are show the top and sideviews of an exemplary stack 2000 of EMP actuators. As shown in FIGS. 20(a) and 20(b), exemplary stack 2000 includes substrate 2020, a stronger,larger EMP actuator 2001 and four smaller top EMP actuators 2011-2014.EMP actuators 2001 and 2011-2014 are each independently controlled. FIG.20( c) show a side view of exemplary stack 2000 when EMP actuators 2001and 2014 are activated, while 2013 is kept at its quiescent length.Constrained by substrate 2020, the elongations of actuators 2001 and2014 render them convex. In particular, EMP actuator 2014 pulls theportions of EMP actuator 2001 and substrate 2020 underneath it furtherupward, such that the side of stack 2000 containing EMP actuator 2014reaches a greater height than the portion of stack 2000 including EMPactuator 2013. Thus, as shown in FIG. 20( c), the surface morphology ofexemplary stack 2000 can be modified in several ways by selectivelyactivating EMP actuators 2001 and 2011-2014. In a practical application,the stack of EMP actuators may be many layers, with smaller and weakerEMP actuators being provided as one goes up the stack. Also, althoughexemplary stack 2000 shows EMP actuators of substantially the samethickness, each layer of EMP actuators may have a different thicknessfrom EMP actuators of other layers. By selectively activating the EMPactuators in such a stack, a large number of deformations may beachieved. For a deformation application, different surface morphologiescan be achieved (e.g., circular or “square” domes). For a hapticapplication, the large number of deformations that can be achievedprovide a large number of nuances in the resulting haptic response. Suchnuances can be exploited to communicate different messages to the useraccording to the difference sensations in the resulting experience. Oneexample is related to use the deformable surface to provide a graphicaldisplay.

A new audio speaker application is achieved by providing a number ofindividually controlled EMP actuators positioned according to apre-determined configuration (e.g., in a regular array, as in FIGS. 7-11above, or in even greater number in any configuration). As the EMPactuators are individually activated, the EMP actuators can provide alarge number of audio speakers in close proximity. Such audio speakerscan be excited together to provide audio volume over a large dynamicrange, or they can be excited selectively and with different excitationsignals to provide very complex sound reproduction.

According to one embodiment of the present invention, multi-layer EMPactuators in a 5×2 array, each comprising ten single-layer actuators,are measured for their respective accelerations, using a triangularvoltage varying over 0-200 volts (peak-to-peak) with a DC-bias or offsetvoltage. A DC offset voltage increases both acceleration andelectromechanical strain. FIG. 17 shows the triangular waveform of thedriving electric field on a multi-layer EMP actuator; the drivingelectric field has a 50 V DC offset voltage and a 200 V peak-to-peakvoltage. The output accelerations of a multi-layer EMP actuator withinthe 5×2 array under DC-offset voltages of 0 volts, 25 volts, 50 voltsand 75 volts are shown in FIG. 18. As shown in FIG. 18, a 25 volt DCoffset voltage increases the peak acceleration to 6.3 G. The increasedacceleration becomes significant for DC offset voltages exceeding 50volts (i.e., 10 V/μm). In the multilayer EMP actuator of FIG. 18, thepeak acceleration increases from 5.5 G to 10 G as the DC-offset voltageincreases from 0 volts to 75 volts.

FIG. 19 shows surface accelerations for multi-layer actuators comprisingdifferent number of component EMP layers, as a function of input signalfrequency. In the multi-layer actuators of FIG. 19, each component EMPlayer is 5 μm thick. As shown in FIG. 19, at a driving voltage of 200volts, the surface acceleration increases from about 18 G, for aten-layer EMP actuator, to 39 G and 53 G, for a 20-layer multi-layer EMPactuator and 30-layer multi-layer EMP actuator, respectively.

An EMP transducer can also be fabricated in fabrics that can be providedin items of clothing. Such EMP transducer thus may provide clothing withmultimodal functions.

Because of their flexibility and their ease in manufacturing, EMPtransducers can be made very small even on a consumer device (e.g., thetouch surface of a cellular telephone). As a result, tactile feedback inresponse to touch by a human finger may be localized to an area in theimmediate vicinity of the touch stimulus, thereby offering a strongersensation and a finer resolution. This ability to concentrate thetactile feedback to a localized zone under the user finger can alsoreduce the device's power requirement, as the action required may beconfined to a small zone associated with the finger, without involvingthe entire device.

According to one embodiment of the present invention, two or more EMPactuators may be driven simultaneously, each with a varying phase andamplitude in the driving signal. Such an arrangement may create hapticresponses that take advantage of, for example, constructiveinterference. Thus, EMP actuators may be strategically located toprovide an optimized, localized haptic event, based on the additivenature of haptic responses. This technique of haptic event deliveryrelies on analysis of the dynamics of the touch surface, taking intoaccount damping, wave dispersion and other effects. Furthermore,according to one embodiment of the present invention, a touch surfacecan be driven at frequencies that correspond to the resonant modes ofthe touch surface. A driving frequency corresponding to a resonant modecreates a standing surface mode of vibration with points of maximumdisplacement (i.e., anti-nodes) and no displacement (i.e., nodes). Byidentifying the location where a user provides an input stimulus (e.g.,where the user's finger touches the touch surface) and sensing thestrength of the stimulus, if appropriate, a library of predeterminedmode shapes may be searched for the driving mode which provides theappropriate response (e.g., the largest anti-node at the position oftouch).

Therefore, according to one embodiment of the present invention, ahaptic system may integrate one or more EMP actuators, control circuitand software. Application software may have access to such a hapticsystem through an application program interface. In some haptic systems,customized electronics, such as a power amplifier, may be provided todrive the EMP actuators. In handheld devices, the power amplifier relieson a regulated power source (e.g., a regulated 3 volts power supply) aspower source.

FIGS. 21( a) and 21(b) shows conceptually how an EMP sensor operates,according to one embodiment of the present invention. As shown in FIG.21( a) EMP sensor 2300 is preferably initially charged by a power sourceor power supply. After EMP sensor 2300 is charged, charge is stored inthe EMP layer or layers of EMP sensor 2300. In the charged state, acontact with EMP sensor 2300 or an application a mechanical force on EMPsensor 2300 would alter the capacitance of the EMP layer (e.g., as shownin FIG. 21( b)) and result in a measurable voltage across (or a currentflowing through) leads 2302 and 2303 of EMP sensor 2300. Although notexpressly shown in FIGS. 21( a) and 21(b), it is understood that EMPsensor 2300 provides a surface that transmits an externally imposedmechanical force to the EMP layers of EMP sensor 2300. In the EMPsensors described above, the measurable voltage may be as high as a fewvolts (e.g. 1-5 volts), making such EMP sensors desirable for use inmany applications (e.g., portable computational devices, such smarttelephones and tablet computers). Charging of the EMP sensor is notrequired in theory. However, without charging, a very sensitive circuitthat can measure minute changes in capacitance in the EMP sensor (e.g.,sensitive to changes in the order of microvolts) would then be required.In another embodiment, the EMP sensor may be charged before beinginstalled in a final device. In some applications, such an EMP sensormay maintain its charge, and hence its sensor performance, without beingcharged again in its lifetime.

FIGS. 22( a) and 22(b) show EMP sensor 2400 provided on the surface ofthin compliant film 2401 (e.g., a thin aluminum or steel film), inaccordance with one embodiment of the present invention. As shown inFIG. 22( a), EMP sensor 2400 is preferably charged by a voltage supplyto a quiescent state. As shown in FIG. 22( b), when a force is appliedon thin compliant film 2401, the change in shape in compliant film 2401stretches the EMP layer or layers within EMP sensor 2400, therebyaltering the capacitance of those EMP layers, resulting in a measurablevoltage or current output from EMP sensor 2400.

Alternatively, FIGS. 23( a) and 23(b) show EMP sensor 2500 provided onthe surface of rigid substrate 2501, in accordance with one embodimentof the present invention. As shown in FIG. 23( a), EMP sensor 2500 ispreferably charged by a voltage supply to a quiescent state. As shown inFIG. 23( b), when a force is applied directly on EMP sensor 2500, theEMP layer or layers within EMP sensor 2500 are deformed by themechanical force experienced, thereby altering the capacitance of thoseEMP layers, resulting in a measurable voltage or current output from EMPsensor 2500. EMP sensor 2500 can therefore be used to directly measure aforce applied on the surface.

In a further configuration, FIGS. 24( a) and 24(b) show EMP sensor 2600placed between the surfaces of two rigid layers 2601 and 2602, inaccordance with one embodiment of the present invention. As shown inFIG. 24( a), EMP sensor 2600 is preferably charged by a voltage supplyto a quiescent state. As shown in FIG. 24( b), when a force is appliedon directly on either of layers 2601 and 2602, the EMP layer or layerswithin EMP sensor 2600 are compressed by the mechanical forceexperienced, thereby altering the capacitance of those EMP layers,resulting in a measurable voltage or current output from EMP sensor2600.

Of importance is the fact that the EMP sensors disclosed herein arebased on polymer films, which are highly flexible. As a result, EMPsensors may be made to conform to any kind of surface, and thus may beeffective force sensors on curved or irregular surfaces, in addition tothe flat surfaces provided in FIGS. 22-24 above.

FIG. 25 shows schematic circuit 2700 in which EMP sensor 2701 is used,in accordance with one embodiment of the present invention. As shown inFIG. 25, EMP sensor 2700 is connected in series with resistor 2702,which is provided to limit the charging and discharging current. Voltagesource 2703 maintains EMP sensor 2700 in a charge state. Sensor outputmeasurement circuit 2704 represents a circuit that is sensitive to avoltage change resulting from a change of capacitance caused by amechanical force applied directly or indirectly on EMP sensor 2701.

FIG. 26 shows schematic circuit 2800 in which EMP sensor 2801 is used,in accordance with one embodiment of the present invention. As shown inFIG. 26, EMP sensor 2800 is connected in series with sensor outputmeasurement circuit 2804 and resistor 2802, which is provided to limitthe charging and discharging current. Voltage source 2803 maintains EMPsensor 2801 in a charge state. Sensor output measurement circuit 2804represents a circuit that is sensitive to a current resulting from achange of capacitance caused by a mechanical force applied directly orindirectly on EMP sensor 2801.

Although the examples herein use resistors as means for indicatingquantitatively a change in the charged state in an EMP sensor, the useof resistors is only one of many ways that can be used. Any suitablemeans for providing a quantitative indication of a change in chargedstate in the EMP sensor may be used, such as an electrometer or anycurrent measurement device.

An EMP sensor disclosed herein in its charged state provides asignificant voltage output in response to the range pressures typicallyencountered in a mobile application, such as a keyboard. Furthermore, asmentioned above, such an EMP sensor can act as an actuator (i.e., unlikean EMP sensor, which receives a mechanical input to provide anelectrical response, an actuator receives an electrical input to providea mechanical response). Suitable placement of switches allowsreconfiguring a circuit with one or more EMP sensors to switch betweensensor and actuator functions. An EMP sensor circuit disclosed hereinmay have dedicated terminals to charge the EMP sensor and separateterminals to receive the electrical output signal. As both an EMP sensorand an EMP actuator according to the present invention, the EMPsensor/actuator may be applicable to analog sensing of touch (e.g., asan analog sensor with at least 3 levels of touch sensing: no sensing,intend to press, button release). In response to the sensed touch, theEMP sensor/actuator provides as a haptic response local sound, localvibration or deformation. The haptic response may also be a programmableblocking force that bears an appropriate relationship (e.g., a linearrelationship) to the sensed pressure. Of course, the EMP sensor/actuatorneeds to be supported by a closed-loop algorithm and drive electronics.Sensing an analog pressure with more than two levels provides a morerealistic and richer user experience. FIG. 27 shows schematic circuit2900 in which control circuit 2901 receives from EMP sensor/actuator2902 sensing signal 2903, representative of the tactile pressureexperienced at EMP sensor/actuator 2902 and provides a haptic responsethrough actuating signal 904, in accordance with one embodiment of thepresent invention.

FIG. 28 illustrates system 1000 in which EMP transducer 1004 performsboth actuation and sensing operations, in accordance with one embodimentof the present invention. As shown in FIG. 28, system 1000 includes EMPtransducer 1004, controller 1001, driving circuit 1002, charging circuit1003, switching circuit 1005, and sensing circuit 1006. Initially,controller 1001 sets switching circuit 1005 to connect charging circuit1003 to EMP transducer 1004 to charge EMP transducer 1004 in preparationof its sensing operations, in the manner such as illustrated by any ofthe sensing operations discussed above. EMP transducer 1004 may be, forexample, a pressure sensor. When charging of EMP transducer 1004 iscomplete, controller 1001 sets switching circuit 1005 to connect EMPtransducer 1004 to sensing circuit 1006. Controller 1001 then monitorssensing circuit 1006 for any occurrence of a sensed event at EMPtransducer 1004. When such an event is detected, controller 1001analyzes the event to determine an appropriate response (e.g., a hapticresponse). To effectuate the response, controller 1001 sets switchingcircuit 1005 to connect EMP transducer 1004 to driving circuit 1002.Controller 1001 then causes driving circuit 1002 to provide a suitabledriving signal for the appropriate response to EMP transducer 1004. Thedriving signal causes EMP transducer 1004 to provide the intendedresponse in a manner such as any of the actuation operations discussedabove (e.g., a haptic vibration or sound).

The above detailed description is provided to illustrate the specificembodiments of the present invention and is not intended to be limiting.Numerous variations and modifications within the scope of the presentinvention are possible. The present invention is set forth in thefollowing claims.

We claim:
 1. An electromechanical system, comprising: an EMP transducer;a driving circuit; a sensing circuit; a switching circuit; and acontroller circuit which directs the switching circuit (a) to connectthe EMP transducer to the sensing circuit to conduct a sensingoperation, and (b) upon detecting a sensed event at the sensing circuit,to connect the EMP transducer to the driving circuit, which provides anactivation signal under control of controller to the EMP transducer toperform an actuator function.
 2. The electromechanical system of claim1, further comprising a charging circuit, for charging circuitconnectable by the switching circuit to the EMP transducer, for chargingthe EMP transducer prior to a sensing operation.
 3. Theelectromechanical system of claim 1, wherein the EMP transducercomprises EMP layers based on an electrostrictive polymer and a forcereceiving surface that transmits a mechanical force to the EMP layer,and wherein the sensing operation comprises detecting a mechanical forceat the force receiving surface.
 4. The electromechanical system of claim3, wherein the electrostrictive polymer comprises one or more polymersselected from the group consisting of a polymer, copolymer, orterpolymer of vinylidene fluoride.
 5. The electromechanical system ofclaim 3, wherein the electrostrictive polymer comprises a polymerselected from a group of polymers consisting of:P(VDF_(x)-TrFE_(y)-CFE_(1-x-y)) (CFE: chlorofluoroethylene),P(VDF_(x)-TrFE_(y)-CTFE_(1-x-y)) (CTFE: chlorotrifluoroethylene),Poly(vinylidene fluoride-trifluoroethylene-vinylidede chloride)(P(VDF-TrFE-VC)), poly(vinylidenefluoride-tetrafluoroethylene-chlorotrifluoroethylene) (P(VDF-TFE-CTFE)),poly(vinylidene fluoride-trifluoroethylene-hexafluoropropylene),poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene),poly(vinylidene fluoride-trifluoroethylene-tetrafluoroethylene),poly(vinylidene fluoride-tetrafluoroethylene-tetrafluoroethylene),poly(vinylidene fluoride-tri fluoroethylene-vinyl fluoride),poly(vinylidene fluoride-tetrafluoroethylene-vinyl fluoride),poly(vinylidene fluoride-trifluoroethylene-perfluoro(methyl vinylether)), poly(vinylidene fluoride-tetrafluoroethylene-perfluoro(methylvinyl ether)), poly(vinylidenefluoride-trifluoroethylene-bromotrifluoroethylene, polyvinylidene),poly(vinylidene fluoride-tetrafluoroethylene-chlorofluoroethylene),poly(vinylidene fluoride-trifluoroethylene-vinylidene chloride), andpoly(vinylidene fluoride-tetrafluoroethylene vinylidene chloride), wherex has a value in the range between 0.5 and 0.75, y has a value in therange between 0.45 and 0.2.
 6. The electromechanical system of claim 3,wherein the electrostrictive polymer comprises a P(VDF-TrFE-CFE) orP(VDF-TrFE-CTFE) terpolymer.
 7. The electromechanical system of claim 3,wherein the electrostrictive polymer comprises a high energy electronirradiated P(VDF-TrFE).
 8. The electromechanical system of claim 3,wherein the electrostrictive polymer comprises a blend ofelectrostrictive polymers with PVDF and PVDF copolymers.
 9. Theelectromechanical system of claim 8, wherein the blend includes one ormore of P(VDF-CTFE), P(VDF-HFP), P(VDF-CFE), P(VDF-TrFE), and P(VDF-TFE)polymers.
 10. The system of claim 3, further comprising a forcereceiving surface structurally connected with the EMP transducer fortransmitting an external force to the EMP layers.
 11. The system ofclaim 10, further comprising a substrate bonded to one side of one ofthe EMP transducers.
 12. The system of claim 10, wherein the externalforce exerted on the force receiving surface results in an electricalsignal being induced across a pair of electrodes.
 13. The system ofclaim 12, wherein the electrical signal is between 0.001 volts to 100volts.
 14. The system of claim 12, wherein the electrical signal isbetween 0.001 volts to 10 volts.
 15. The system of claim 12, wherein theelectrical signal is between 0.001 volts to 5 volts.
 16. The system ofclaim 12, wherein the sensing circuit senses the electrical signal andsends a signal to the controller circuit.
 17. The system of claim 16,wherein the sensing circuit comprises a resistor and a circuit forsensing a voltage change across the resistor.
 18. The electromechanicalsystem of claim 1, wherein the EMP transducer can deform an attachedsurface.
 19. The electromechanical system of claim 1, wherein theactuator function comprises providing a vibration at a frequency between50 Hz to 400 Hz.
 20. The electromechanical system of claim 1, whereinthe actuator function comprises providing an audible sound within anacoustic range.
 21. The electromechanical system of claim 1, wherein theEMP transducer comprises a plurality of EMP layers each having athickness less than 10 um and electrodes configured such that the EMPlayers are connected in parallel for the sensing operation and theactuator function.
 22. The electromechanical system of claim 21, whereinthe EMP layers in the EMP transducer are of different thicknesses. 23.The electromechanical system of claim 21, wherein the EMP transducer hasEMP layers that are of different sizes.
 24. The electromechanical systemof claim 21, wherein the EMP layers are each between 0.1 um to 10 umthick.
 25. The electromechanical system of claim 24 wherein at least oneof the EMP layers is 5 microns thick or less.
 26. The electromechanicalsystem of claim 24, wherein at least one of the EMP layers is 3 micronsthick or less.
 27. The electromechanical system of claim 24, wherein theEMP transducer comprises multiple component transducers stackedtogether, the component transducers being of a different size, adifferent layer thickness, or a different number of EMP layers relativeto each other.
 28. The electromechanical system of claim 1, wherein theEMP transducer has a response latency of less than 40 milliseconds. 29.The electromechanical system of claim 1, wherein the EMP transducer hasa decay time of less than 40 milliseconds.
 30. The electromechanicalsystem of claim 1, wherein the EMP transducer is transparent.
 31. Theelectromechanical system of claim 1, wherein the EMP transducer issemitransparent.
 32. The electromechanical system of claim 1, whereinthe EMP transducer is opaque.